1. Field of the Invention
The present invention relates generally to exposure apparatuses, and more particularly, to an exposure apparatus used in manufacturing a semiconductor device and a method of exposure using the exposure apparatus.
2. Description of the Background Art
Recently, photolithography is an indispensable technology in manufacturing semiconductor devices.
With semiconductor devices miniaturized, an exposure apparatus of higher accuracy has been required. As for an example of a conventional exposure apparatus, description will be given to a technology disclosed in Japanese Patent Laying-Open No. 63-274131 hereinafter.
Referring to FIGS. 5 and 6, description will be given to the structure of a photomask 101 with pellicle having a pellicle provided serving as an anti-particle film based on a conventional technique. FIG. 5 is a plan view of photomask 101 with pellicle. FIG. 6 is a cross section taken along the line X--X in FIG. 5. Photomask 101 with pellicle has a pattern 115 of a predetermined shape formed on the surface, opposite to the surface for receiving exposure light, of a substrate 111 of glass or the like. Pellicle films 113, 114 generally include nitrocellulose as the main constituent. Pellicle film 113 is attached to an upper side film frame 116 and a lower side film frame 117. Upper side film frame 116 and lower side film frame 117 are attached to substrate 111. A distance h.sub.1 from pellicle film 113 on the upper side to the surface of the substrate is set to approximately 4.0 mm. A distance h.sub.2 from pellicle film 114 on the lower side to the surface of the substrate is set to approximately 6.3 mm.
Even if a foreign matter Z having a diameter of approximately 50.mu.m attaches onto pellicle film 114, the shadow of the foreign matter Z in exposure is defocused on the semiconductor substrate. Therefore, it is possible to carry out exposure without affecting transfer to the semiconductor substrate.
A window portion 118 for measuring an amount of exposure is provided in a predetermined portion of substrate 111 in a region enclosed by pellicle films of photomask 101 with pellicle.
Description will now be given to an exposure apparatus 100 including photomask 101 with pellicle.
Referring to FIG. 7, exposure apparatus 100 includes a mask stage 102, a mask loader 103, an exposure light source 106, a projection optical system 107, a wafer stage 105 and a scanning carriage 109. Photomask 101 with pellicle is disposed between exposure light source 106 and projection optical system 107. A semiconductor wafer 104 is disposed on wafer stage 105.
Referring to FIG. 8, description will be given to a first operation of exposure apparatus 100. First, instruction to load photomask 101 with pellicle is given from a controller (not shown) provided in exposure apparatus 100. Before setting photomask 101 with pellicle on mask stage 102, scanning carriage 109 is moved in a direction of an arrow A shown in the figure. Then, exposure luminous flux 108 is directed from exposure light source 106. Exposure luminous flux 108 is focused on a light receiving element 110 for measuring an amount of exposure set at the same height as the surface of semiconductor wafer 104. The amount of exposure at this time is measured by light receiving element 110 for measuring an amount of exposure. The amount of exposure when photomask 101 with pellicle is not provided is stored as "A".
Referring to FIG. 9, description will be given to a second operation of exposure apparatus 100. Photomask 101 with pellicle is set on mask stage 102. Then exposure luminous flux 108 is directed from exposure light source 106. Exposure luminous flux 108 is first focused on photomask 101 with pellicle. Window portion 118 for measuring an amount of exposure is provided with photomask 101 with pellicle in a position corresponding to light receiving element 110 for measuring an amount of exposure. Therefore, exposure luminous flux 108 transmits window portion 118 for measuring an amount of exposure to be focused on light receiving element 110 for measuring an amount of exposure. The amount of exposure at this time is stored as an amount of exposure "B" when exposure luminous flux 108 transmits photomask 101 with pellicle.
The value of a ratio B/A (where A is the amount of exposure when exposure luminous flux 108 does not transmit photomask 101 with pellicle and B is the amount of exposure when exposure luminous flux 108 transmits photomask 101 with pellicle is indicated as transmittance T of the pellicle.
When the transmittance T is lower than a predetermined Tc, it is possible to inform the user of the pellicle film life.
However, in the above-described conventional technique, the value A measured without a photomask is used for finding the transmittance T. Therefore, decrease of exposure light caused by the glass substrate is ignored in the value A.
Furthermore, since the transmittance T is set without considering decrease of the amount of exposure by degradation of the exposure light source, there is sometimes a problem that even a pellicle film which can be still usable must be changed for another one.